Prosthesis structures of the type defined are known for use in human knee-joint replacement surgery from prior patent application publications FR-A-2630639 (Le Beguec) and WO93/22990 (Astra AB) with the prosthesis structures made known therein being for anchorage in the knee-joint end of a human tibia or femur respectively. In the prosthesis structures of FR-A-2630639 and WO93/22990 the longitudinal axis of the fixture is oriented parallel to the engagement surface. WO93/22990, the contents of which are incorporated herein by reference, further discloses orienting the fixture at an angle to the main articulation plane of the knee-joint which extends between the extension or anterior side of the joint and the flexion or posterior side of the joint.
The aim of the present invention is to adapt the relation between the elongate fixture and the engagement surface of a prosthesis of the type defined for improving the anchorability of the prosthesis structure.